Effect of the GnRH antagonist, acyline, on canine testicular characteristics

The primary objective was to assess the effects and clinical safety of a single high-dose of the third generation GnRH antagonist, acyline, on testicular characteristics in male dogs. Seven dogs were followed up weekly for six, 2-week periods (−2, −1, 1, 2, 3 and 4). At the end of the second period, they were given acyline (330 μg/kg sc). Responses to treatment varied among individual animals. Testicular consistency and scrotal diameter were slightly diminished (P > 0.05) in Periods 1, 2, and 3. Libido and erection decreased during Periods 1 and 2 (P < 0.05). Second and third fractions of the ejaculate volume, sperm count and motility varied throughout periods (P < 0.01); there was a clear impairment of these parameters (≤0.2 mL, ≤0.6 mL, ≤0.5 million/mL and ≤30%, respectively) around the second week of Period 1, followed by slow improvement (to the end of the study). Semen volumes and motility diminished during Period 1 (P < 0.05). Sperm count decreased during Periods 1, 2, and 3, relative to Periods −2 and −1 (22.7 ± 11.7, 62.8 ± 19.9, and 51.0 ± 25.4 versus 235.7 ± 63.3 and 315.5 ± 27.3, respectively; P < 0.05; (L.S.M. ± S.E.M.). Morphologically abnormal sperm increased during Periods 2 and 3 (up to 64.9 ± 2.6%; P < 0.05). Throughout the study, no dog had hematological, biochemical, local, or systemic side effects. In conclusion, a single high-dose acyline treatment severely decreased semen quality with no adverse effects.